A protester reacts as water mixed with tear gas liquid is sprayed by police water canon to disperse protesters during an anti-government rally in central Seoul, South Korea, November 14, 2015.Kim Hong-Ji

SEOUL (Reuters) - Tens of thousands protested against South Korean President Park Geun-hye's labor and education policies on Saturday in one of the largest street rallies in recent years, prompting police to use water canons and barricades to stop the crowd.

A militant labor federation, with a diverse membership spanning trucking, construction, autoworkers and public teachers, organized the rally as the crowd converged in central Seoul and tried to march toward the presidential Blue House.

They were protesting against Park's plans to make the labor market more flexible by giving employers greater leeway in dismissing workers and her decision for a government-selected panel to write the high school history textbook.

Rally organizers demanded Park step down. The conservative leader took office in 2013 after a decisive election win over a liberal challenger and is serving a single five-year term.

Han Sang-gyun, the president of the Korean Confederation of Trade Union, who has a warrant for his arrest for organizing previous illegal rallies, called for more protests and a general strike, unless the government withdraws its labor market plan.

"The government must immediately cease worsening labor conditions," Han told the crowd, before scurrying away to avoid being caught by the police.

The police set up roadblocks across the main thoroughfare, blocking protesters from marching toward the Blue House and sprayed water canons into the crowd. Some protesters fought police with steel pipes.

Park had earlier left for Turkey to participate in the summit of G20 nations.